<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>CSS选择器</title>
  <style>
    body {
      padding: 10px;
      font-size: 14px;
      background:red;
    }
    body.body {
      font-size: 20px;
      background: red;
    }
    #body {
      background: blue;
    }
    .body div .hello {
      color: #fff;
    }
  </style>
</head>
<body class="body" id="body">
  Hello CSS!
  <div>
    <a class="hello">test</a>
  </div>
</body>
</html>
